The present invention relates to a method for manufacturing an optical device; and, more particularly, to a method for manufacturing a spot-size converter (SSC) having sharp end tips for use in an optical communication by using distributed pads during the SSC formation.
As is well known, an optical device for use in an optical communication includes an optical fiber, a spot-size converter and a laser diode. A number of methods have been proposed over the years to implement an efficient coupling of the laser diode to the optical fiber because a light beam emitted from the laser diode looses its energy at an interface between the diode laser and the optical fiber.
In order to overcome the above-described problem, there has been proposed an optical device such as a tapered semiconductor structure appear to minimize a loss between the diode laser and the optical fiber. However, the process of manufacturing the tapered semiconductor structure is very complex and consequently requires high alignment accuracy. Therefore, there is a strong demand for manufacturing a tapered semiconductor structure having a small size end tip for removing a mode inconsistency between the optical elements.
In FIG. 1, there is shown a cross sectional view setting forth a conventional semiconductor waveguide 10, disclosed n U.S. Pat. No. 5,720,893, entitled xe2x80x9cTAPERED BEAM EXPANDER WAVEGUIDE INTEGRATED WITH A DIODE LASERxe2x80x9d. The semiconductor optical device 10 includes a first waveguiding layer 13 formed on top of a substrate, an etch stop layer 11 and a second waveguide layer 12.
The conventional semiconductor waveguide 10 must utilize two steps of patterning processes in order to obtain a lateral tapered structure. Specifically, a first knife-edge mask is applied to a left-section of the second waveguide layer 12, thereby removing a right-section of the second waveguide 12. After an etchant is deposited on the second waveguide layer 12, the right-section is etched away to leave only the left-section. Subsequently, a second knife-edge mask is applied to a portion 20 of the left-section. An etchant again deposited on the second waveguide layer 12 to etch away the remaining portion of the left-section. As a result of the etching of the remaining portion, the second waveguide layer 12 is now reduced to the area shown in FIG. 1 as the portion 20.
Even though the aforementioned semiconductor optical device 10 and the method for the manufacture thereof are capable of reducing its size of end tip, it still suffers from a bad adhesion at end portion of the second waveguide layer 12 and the stop etch layer 11 due to a strain caused by a photoresist layer formed thereabove.
Furthermore, since the patterned left-section of the second waveguide layer 12 has an oblique side wall and the amount of reflected light beam from an interface between the stop etch layer and the left-section of the second waveguide layer 12 is not uniform, the conventional method requires a very high alignment accuracy during the second patterning process.
These problems, therefore, tend to make it difficult to obtain the desired reproducibility, reliability and yield.
It is, therefore, an object of the present invention to provide a method for manufacturing an optical device for use in an optical communication, which utilizes a pair of strain distributed pads during the formation of a tapered structure, thereby reducing fabrication cost and increasing reproducibility, without utilizing a high resolution electron beam lithography and a stepper.
It is another object of the present invention to provide a method for the fabrication of a spot-size converter with a lateral-tapered structure, which is suitable to reduce a fabrication cost, increase a reproducibility and yield.
It is still another object of the present invention to provide an optical device, which is integrated with the spot-size converter fabricated by the above.
In accordance with one aspect of the present invention, there is provided a photolithography reticle for patterning a tapered pattern into an optical waveguide, which has a lateral-tapered shape at its both distal ends and a wide region of strain relaxation pad connected to the distal ends.
In accordance with another aspect of the present invention, there is provided a method for manufacturing an optical device, comprising the steps of: a) forming a waveguide layer on a semiconductor substrate; b) forming a mask layer and patterning the mask layer into a predetermined configuration in such a way that the predetermined configuration has a taper portion at its both distal ends and a pair of strain distributed pads; c) etching the waveguide layer using the patterned mask layer as an etching mask; and d) removing the patterned mask layer and subsequently removing portions of the waveguide layer corresponding to the strain distributed pads, thereby obtaining a tapered waveguide.
In accordance with still another aspect of the present invention, there is provided a method for the fabrication of a spot-size converter, comprising the steps of: a) forming a first waveguide layer, a first cladding layer, a second waveguide layer and a second cladding layer on a semiconductor substrate, sequentially; b) forming a mask layer on the second cladding layer and patterning the mask layer into a predetermined configuration in such a way that the predetermined configuration has a taper portion at its both distal ends and a pair of strain distributed pads; c) etching the second cladding layer and the second waveguide layer by using the patterned mask layer as an etching mask; and d) removing the patterned mask layer and subsequently removing portions of the second cladding layer and the second waveguide layer corresponding to the strain distributed pads, thereby obtaining a tapered waveguide on top of the first cladding layer.